In bearing assemblies, such as rolling element bearings, there is often a need for monitoring the conditions of the components in order to determine the status of the components and possibly predict future failures. Monitoring the conditions is particularly important for bearing assemblies since they are used under extreme operating conditions which in turn result in that the materials and components are heavy-loaded. Various measurements can be used for monitoring the conditions of the components in a bearing assembly.
One particularly critical component in a bearing assembly is the lubricant, e.g. oil or grease. The main purpose of the lubricant is to prevent metallic contact between the rolling elements, raceways and cages and thus to prevent wear of the bearing assembly. The lubricant is also used for cooling and to protect the bearing surfaces against corrosion. Accordingly, it is central that the condition of the lubricant is monitored in order to ensure a reliable operation of the bearing assembly. That is, by measuring and monitoring the condition of the lubricant, it is possible to early detect if there is an insufficient lubrication.
It has been observed that in certain circumstances, the metallic contact, i.e. the asperity contacts, between the bearing raceway surface and the bearing rolling element may generate acoustic emissions (AE). Moreover, acoustic emissions can occur due to contamination within the lubricant, other metallic noise sources, roller skewing or skidding. Acoustic emissions may also result from the initiation and growth of cracks, slips and dislocation movements, twinning, or phase transformations in metals. Hence, acoustic emission generated from various sources is regarded as one significant and measurable indication of the condition of a bearing assembly. In view of this, there is an increasing demand for monitoring acoustic emissions in a bearing assembly.
As an example, acoustic emission measurements can be obtained by mounting an acoustic emission pickup sensor directly onto a bearing outer ring surface of a bearing assembly. Conventionally, this is carried out by attachment of the acoustic emission pickup sensor in a predefined groove or space in the radial plane of the outer ring. The attachment of the AE pickup sensor can for instance be done by gluing or by using pressure such that the sensor is firmly maintained on the bearing ring surface.
However, due to the construction of the bearing assembly, minor space is left for additional components in the bearing housing. It is therefore often problematic to mount various monitoring equipments and sensors in the bearing assembly, while maintaining a high level of accuracy and quality in the measurements. Accordingly, there is a need for an alternative solution for monitoring the conditions of a bearing assembly enabling improved and accurate acoustic emission measurements. In particular, it is desirable that a balance is kept between the size and the functionality of the monitoring components such that measurements can be carried out in mass-produced bearing assemblies.